Place pears, apple, orange, cane syrup, 2 tablespoons vanilla, ginger, cloves, allspice, cinnamon, and cardamom into a 6-quart slow cooker. Add 8 cups water.
Cover and cook on high until fruit is very soft and cider has slightly deepened in color, 4 hours.
Strain cider through a fine-mesh sieve. Reduce slow cooker setting to warm and return cider mixture to slow cooker. Add remaining 2 tablespoons vanilla and lemon juice. Keep warm until ready to serve. Garnish with apple, orange, pear, and cinnamon, if desired.